Apparatus for determining stem content of tobacco



March 8, 1966 J. 1-. ASHWORTH ETAL 3,233,952

APPARATUS FOR DETERMINING STEM CONTENT OF TOBACCO Filed April 17, 1964 r- I E 5; \o 42. ,Tf W1 4 m 8 INVENTORI, gfl/V ASHWQETH 6. BROOKS U CAssm United States Patent 3,238352 APPARATUS FOR DETERMINING STEM CONTENT OF TOBACCG John T. Ashworth, John G. Brooks, and Bruce P. Cassidy, Richmond, Va, assignors to The American Tobacco Company, New York, N.Y., a corporation of New Jersey Filed Apr. 17, 1964, Ser. No. 360,625 5 Claims. (Cl. 131-446) This invention relates to improved apparatus for quickly determining the stem content of strip tobacco so as to enable the stemming process to be effectively controlled.

Strip tobacco consists of leaves that have been stemmed, that is, not only the stem proper but the midrib, or central vein, has been removed. The term stem as used in this specification includes both the stem and the central vein or midrib, while the term leaf includes the small or branch veins. It is important to control the stemming process so that the correct amount of stem will be removed because an over percentage of stem will tend to degrade the final product, whereas the removal of too large a percentage is uneconomical.

Heretofore two principal methods of determining the stem content of strip tobacco have been employed namely hand stemming, and the ball mill method. The former is inaccurate and requires considerable time to make a determination. The latter method also requires an excessive amount of time, although it is accurate. The disadvantages of these prior methods have been overcome by the improved apparatus of the present invention so that an accurate determination of the stem content can be made within as short a time as five minutes. In this way the operator is enabled to effect changes in the stemming operation so as to properly control the stem content of the strip tobacco.

Although the invention has been developed to determine the stem content of tobacco, it can also be employed more generally, as for example, in examining any friable product having an associated contaminant, provided there is an appropriate difference in the bulk densities of the end product and the contaminant.

In accordance with the present invention, a sample of the friable product and associated contaminant, such as strip tobacco from which the stem has not been entirely removed, is first weighed and then placed in a closed grinding chamber, and a grinding operation is performed for a limited period of time (from 15 seconds to 3 minutes, preferably 1 minute and 30 seconds) so as to thrash the leaf portion from the stem portion and reduce the particle size of the leaf. A rotor having radially projecting blades is arranged to rotate within the grinding chamber and, advantageously, a stationary breaker bar is arranged to cooperate with these blades. Such bar assists in reducing the leaf particle size. The duration of the grinding operation is made sufficient to reduce the particle size of the leaf sutficiently to enable the ground material to be carried or conveyed by means of an air current.

After the grinding operation has been terminated at current of air is sent for a limited time (from 15 seconds to 3 minutes, preferably 1 minute and 15 seconds) through both the grinding chamber and a separation chamber which is also a closed chamber and positioned at a level above the grinding chamber. The air enters the grinding chamber through a perforated door at the bottom, and carries the small particles of leaf and stem through a narrow passage or throat into the seaparation chamber where the relatively lighter portion is separated from the heavier portion (the stem portion). The leaf portion being lighter and having a larger surface area than the stem portion is carried out of the top of the separation chamber and through a suitable duct to an appropriate collection receptacle. The stem particles being heavier and having less surface area than the leaf, remain in the separation chamber until the air fiow stops.

Advantageously the separation chamber is connected to the upper portion of the grinding chamber through a narrow throat, and also the walls of the separation chamber advantageously diverge upwardly from such throat portion. As the mixture of ground material is drawn upwardly by the air current its velocity is caused to increase as it passes through the narrow throat, and immediately thereafter the velocity decreases as the mixture moves upwardly through the separation chamber. Such decrease in velocity enhances the separation of the lighter leaf portion, and the particles of such lighter portion are carried through the outlet at the top of the separation chamber and into the duct previously referred to. At the same time the heavier particles, that is, the stem portion, fall toward the lower section of the separation chamber, and when the air current is cut off, fall back into the grinding chamber. These relatively heavy stem particles are then removed through a suitable door at the bottom of the grinding chamber. In this way, the amount of the stem material can be accurately determined by weighing, and compared with the weight of the sample of the material which was introduced into the grinding chamber at the commencement of the process.

The purpose is to remove the lighter ground material, that is, the leaf particless from the superposed separation chamber-grinding chamber combination, leaving only the relatively heavy stem particles of the ground material therein, which are allowed to settle through the narrow throat to the bottom of the grinding chamber so that these may be removed and weighed. The weight of this material compared with the weight of the sample is a measure of the percentage of stem contained in the strip tobacco.

One form of apparatus according to the invention is shown in the single diagrammatic drawing which accompanies this application.

Referring to this drawing the grinding chamber is indicated at 1 and as shown is kidney shaped in end view, but in side view is elongated and its lengthwise dimension is sufiicient to receive a sample of strip tobacco ranging from about 6 ounces in weight to about 18 ounces depending upon the type of tobacco. The volume of the tobacco sample should not be either too small or too large. If it is too large the sample will not be ground adequately within the time allowed for the operation and there will be a tendency to block at the throat during the separation operation. The sample is introduced through an opening in the side of the chamber which is closed by means of a hinged door 2 equipped with a suitable latch.

In the lower portion of chamber 1 a rotary grinder 3 is arranged to rotate on a shaft 4 which is driven by an electric driving motor 5. Grinder 3 comprises a drum 6 fixed to shaft 4 and having a lengthwise series of projecting blades 7. These blades may be mounted in either a fixed or flexible position on the drum, and they cooperate with a stationary breaker bar 8 which is mounted at a suitable position on the interior wall of chamber 1 with a clearance of approximately 0.25 inch between the tips of the blades and bar 8.

Below grinder 3 there is a discharge gate 9 for the relatively heavy particles. This gate is hinged at one side and provided at its opposite side with a latch, neither of which is shown. Discharge gate 9 is perforated throughout its surface by holes having a diameter of about 2 mm. for purposes which will appear later on.

The separation chamber is indicated at It) and is disposed above and advantageously at one side of the grinding chamber 1. The walls 11 of the separation chamber are connected through a narrow throat 12 with the walls of the grinding chamber 1. The walls of the grinding chamber gradually approach one another below the throat 12, and the walls 11 of the separation chamber first abruptly and then gradually recede or diverge from one another above throat 12 to the top of the chamber.

At the top of separation chamber 10 there is a hood 13 which connects with a duct 14 leading to the intake of a fan 15, the outlet of which is connected with a bag 16 of porous material forming a collection chamber. Fan 15 is driven by an electric motor 17 through a variable speed gear mechanism 17a.

Electric power for operating motors and 17 is received through supply conductors 18 by two control boxes 19 and 20. Box 19 is connected to motor 5 through conductors 21 and box 20 to motor 17 through conductor 22. Each of these control boxes includes suitable timing mechanism arranged to operate the respective motors for a predetermined period of time, such as for example 2% minutes for motor 5 and 1% minutes for motor 17, and the arrangement is such that the grinding motor 5 operates first and continues to operate throughout the test. After a predetermined period of time, say 1 /2 minutes, the air current motor 17 commences its operation and continues for a period of 1% minutes, after which both motors stop and the sample separation is completed.

Like the grinding chamber 1, separation chamber is elongated in the direction at right angles to the plane of the drawing and has the same width dimension as the grinding chamber.

In operating the apparatus to determine the stem content of the tobacco, a sample within the weight range indicated above is first weighed and then introduced through the door 2, and the control box 19 is activated to start motor 5. The operation of grinder 3 thrashes the leaf material from the stem material and reduces the particle size of both to a predetermined extent depending upon the time of operation and the character of the grinder. During this operation some of the fine particles of the lighter weight leaf material pass through the 2 mm. perforations in the discharge gate 9, and a dust chute 23 attached to the discharge gate directs the dust into any suitable collection unit (not shown).

At the end of the grinding period, the grinder 3 continues to rotate for the purpose of circulating the ground mixture and motor 17 is automatically energized, so that a current of air is drawn in through the perforations in gate 9 to carry the mixture of ground material of both the leaf particles and the stem particles upwardly through the narrow venturi throat 12 and into the separation chamber 10. As the material approaches throat 12, the velocity of the air stream and the mixture suspended therein increases because of the gradually contracting sidewalls of the grinding chamber 1. As the current rises above throat 12 the velocity suddenly decreases because of the abrupt widening of the upper portion of throat 12 and lower portion of walls 11 of the suspension chamber. This reduction in velocity enables the separation of the relatively heavier particles of the stem material from the lighter particles of the leaf material to occur, and this latter material is carried upwardly to the top of the separation chamber and into the duct 14. Traversing this duct it passes through fan and into the collection receptacle 16.

The velocity drop is dependent on the ratio of B to A, where B represents the widest area in the separation chamber 10 and A represents the minimum area in the throat 12.

The velocity of the air of A has to be above a minimum level in order to lift the ground leaf and stems from the grinding chamber 1 into the separation chamber 10. At point B the air velocity has to be such that it will lift the leaf into the discharge duct 14 and leave the stems in chamber 10.

The ratio of B to A is also affected by C which represents the height of the separation chamber from A to B. C must be above a minimum height to prevent the stems eing thrown into the discharge duct 14 due to the velocity that is imparted to them at point A. As C increases above the minimum, the ratio of B to A can decrease. However, the closer the ratio approaches 1 to l, the more critical the air velocities become.

The relative values of C, B and A used in the apparatus are: C=l0.6, 3 4.8 and A=l.0. These can be varied within a reasonable range and still obtain an effective separation.

Upon the completion of the air current operation, the heavier stem particles fall by gravity downward through the throat 12 and through the grinding chamber 1 and collect on the perforated surface of discharge gate 9. This gate is then opened and such material removed and weighed. To the weight, a correction factor, which is a constant value, is added to correlate the results with any standard method. The percentage of stem material is calculated by the following equation:

Percent stems:

It will be understand that the moisture content of the sample is taken into account. Ordinarily, the moisture content of the strip tobacco as prized into hogsheads at the stemmeries is from 10 to 12%, and the sample is weighed at this moisture content. However, if desired, the apparatus will process tobacco having from 8 to 14% moisture content without any change in the operating conditions. By making changes in the operating conditions, the apparatus will process tobacco from a bone-dry condition to the higher moisture content tobaccos customarily encountered in plant processing.

After the collection bag 16 has been emptied to remove the leaf material deposited during the test, the unit is ready for the next test.

Separation chamber 10 is offset from the center line of grinding chamber 1 to prevent any possibility of the rotor 3, which rotates in a clockwise direction, throwing stem material directly through the separation chamber and into the entrance to the duct 14. The bulge in the lefthand wall of grinding chamber 1 as shown in the drawing also assists in preventing such discharge of the stem material.

We claim:

1. Apparatus for determining the stem content of strip tobacco which comprises a grinding chamber in which a predetermined sample of the strip tobacco is confined, means for grinding the sample to thrash the leaf from the stems, a separation chamber above the grinding chamber and having an upwardly increasing cross-sectional area, means for forcing air through the ground sample for a predetermined time to lift the ground sample as a whole into the separation chamber, and means operating for a predetermined time for removing the particles of the relatively light leaf portion from the separation chamber, the particles of the relatively heavy stem portion thereafter returning by gravity to the grinding chamber to be removed therefrom and the amount thereof determined.

2. Apparatus for determining the stem content of strip tobacco which comprises an assembly including a grinding chamber in which a predetermined sample of the strip tobacco is confined, a separation chamber disposed thereabove and connected thereto by a narrow throat, means within the grinding chamber for grinding the sample to thrash the leaf from the stems, means for supplying a current of air upwardly through the assembly so as to carry substantially the entire ground sample through the narrow throat into the separation chamber, the separation chamber having an upwardly increasing cross-sectional area and the velocity of the air current after passing the throat decreasing but still being sufiicient to support and retain the relatively heavy stem portion of the particles within the separation chamber, the current of air having sufiicient velocity at the top of the separation chamber to carry the particles of the relatively light leaf portion out of said chamber, and means for cutting off the air current and allowing the relatively heavy stern portion to descend by gravity into the grinding chamber.

3. Apparatus for deter-mining the stem content of strip tobacco as set forth in claim 2 in which the narrow throat and the separation chamber are oifset from the grinding chamber in the direction of flow so as to prevent ground particles from being thrown by the grinding means into the separation chamber.

4. Apparatus for determining the stem content of strip tobacco which comprises an assembly including a grinding chamber for confining a predetermined sample of the strip tobacco, a separation chamber disposed thereabove the bottom of which is above the top of the grinding chamber, a connecting passageway between the top of the grinding chamber and the bottom of the separation chamber, means within the grinding chamber for grinding the sample to thrash the leaves from the stems while the predetermined sample remains within the grinding chamber, means for supplying a current of air upwardly through the grinding and separation chambers thereby carrying substantially the entire ground sample through the passageway into the separation chamber and leaving the grinding chamber empty, the separation chamber being disposed in vertical position and upwardly increasing in cross-sectional area, and the velocity of the air current after entering the separation chamber decreasing sufiiciently to allow the relatively light leaf portion of the particles to move to the top of the chamber while supporting and retaining the relatively heavy stem portion within the separation chamber, the air current having sufficient velocity at the top of the separation chamber to carry the particles of the relatively light leaf portion out of said chamber, timing means for operating the grinding means, and timing means for operating the air current supply thereby cutting off the air current and allowing the relatively heavy stem particles to return by gravity to the grinding chamber.

5. Apparatus for determining the stem content of strip tobacco which comprises an assembly including a grinding chamber for confining a predetermined sample of the strip tobacco, a separation chamber disposed therea'oove the bottom of which is above the top of the grinding chamber, a connecting passageway between the top of the grinding chamber and the bottom of the separation chamber including a venturi throat, means within the grinding chamber for grinding the sample to thrash the leaves from the stems while the predetermined sample remains within the grinding chamber, means for supplying a current of air upwardly through the grinding and separation chambers thereby carrying substantially the entire ground sample through the venturi throat into the separation chamber and leaving the grinding chamber empty, the separation chamber being disposed in vertical position and upwardly increasing in cross-sectional area, and the velocity of the air current after passing the throat decreasing abruptly causing separation of the particles of the relatively light leaf portion from the particles of the relatively heavy stern portion, the air current having sufficient velocity to carry the particles of the relatively light leaf portion out of said chamber, and means for cutting off the air current and allowing the relatively heavy stern portion to return by gravity to the grinding chamber,

References Cited by the Examiner UNITED STATES PATENTS 384,565 6/18-88 Drummond 131-146 384,566 6/1888 Drummond 131-146 656,481 8/1900 Scholtz 131-146 X 1,797,434 3/1931 McLaughlin et al. 241-52 X 1,807,923 6/ 1931 Lykken 241-52 X 2,050,765 8/1936 Rundell 13'1-146 X 2,173,087 9/ 1939 Eissmann 131-146 2,826,205 3/1958 Eissmann 131-146 2,931,581 4/1960 Lykken et al. 241-52 2,991,948 7/1961 Humrnelen 241-7 3 3,128,775 4/1964 Eissmann 131-146 FOREIGN PATENTS 670,410 1/ 1939 Germany. 682,172 10/1939 Germany.

SAMUEL KORE'N, Primary Examiner.

H. P. DEELEY, IR., AssistantExaminer. 

1. APPARATUS FOR DETERMINING THE STEM CONTENT OF STRIP TOBACCO WHICH COMPRISES A GRINDING CHAMBER IN WHICH A PREDETERMINED SAMPLE OF THE STRIP TOBACCO IS CONFINED, MEANS FOR GRINDING THE SAMPLE TO THRASH THE LEAF FROM THE STEMS, A SEPARATION CHAMBER ABOVE THE GRINDING CHAMBER AND HAVING AN UPWARDLY INCREASING CROSS-SECTIONAL AREA, MEANS FOR FORCING AIR THROUGH THE GROUND SAMPLE FOR A PREDETERMINED TIME TO LIFT THE GROUND SAMPLE AS A WHOLE INTO THE SEPARATION CHAMBER, AND MEANS OPERATING 